Can I Use Any Landline Phone with My BT Homehub?

My parents recently switched their landline to VOIP and got a new BT Homehub with some changes in how everything is plugged in. The only connections to the Homehub are a power cable and a phone line. There's also an old cordless phone linked to a power socket that uses two plugs—one for power and the other is a BT-branded box connecting to the mains. The current phone isn't charged anymore, so they want to buy a new one. However, they're confused about whether they need a 'VOIP Compatible' phone or if standard phones would work. Additionally, it seems like there's a BT socket on the Back of the Homehub that might accept a standard phone connection. Would any landline phone work with it? And is the BT Homehub somehow functioning like an Ethernet over Power system?